This invention relates to a positive temperature coefficient resistor package and more particularly to a package containing a PTCR ceramic slug with glass bonded aluminum electrodes being electrically connected by pressure contacts from two identical unitary resilient metal pieces that also provide space terminal and pin socket functions.
PTCR resistors are commonly connected in series with the auxillary or start winding of a motor. Such PTCR resistors have a low resistance at room temperature but when the temperature is raised above the characteristic anomally temperature (typically 120.degree. C.) they present a high resistance. The circuit is first activated, a large current flows (typically for 0.25 seconds) before by self heating the PTCR resistor body becomes highly resistive effectively reducing the current in the start winding one or more orders of magnitude. A further description of such a system is described in U.S. Pat. No. 3,965,392 issued June 22, 1976 and assigned to the same assignee as is the present invention.
Of special interest here is a PTCR resistor to be used in domestic refrigerators. Such refrigerators commonly employ a heremetically sealed chamber that houses the compressor and motor. Electrical access is had via a glass to metal hermetically sealed header, typically having three equally spaced (usually 0.46 inches or 117 mm.) circular pins of about 0.09 inch or 2.3 mm. diameter. A first and second of these pins may lead to the main winding and the auxiliary winding of the motor respectively, while the third pin is common to the other ends of those windings. Thus, the PTCR resistor is connected across the latter two pins. Refrigerator manufacturers prefer that the PTCR resistor package include sockets that make electrical contact to and also physically mount to the aforesaid latter two pins, and further require that spade terminals be provided by the package to which electrical connection to other parts of the refrigerator control circuit may be had.
The pin socket, slug contacting and spade terminal functions have heretofore been implemented by an assembly of dissimilar metal pieces, that require separate tooling.
It is of major importance that for such applications that the PTCR resistor package be capable of production at very low cost. Pressure contacts rather than solder or otherwise bonded connections to the ceramic slug electrodes are much preferred because of their relatively low cost. However, heretofore only electrodes containing precious metals, usually silver, were suitable for pressure contacting.
It is an object of the present invention to provide a low cost PTCR resistor package containing a PTCR slug with glass bonded aluminum electrodes that are free of precious metals and are pressure contacted.